1. Technical Field
The invention relates to an analog front-end transmitter and a connection method of an x-Digital Subscriber Line having a pre-distortion mechanism.
2. Description of the Related Art
FIG. 1 shows a circuit block diagram illustrating a general x-Digital Subscriber Line (xDSL). The xDSL 100 includes a transmitter 101, a digital signal processor (DSP) 102, a transformer 103 and a receiver 104. The transmitter 101 includes a digital-to-analog converter (DAC) 101a, a transmission filter (TXF) 101b, and a line driver (LD) 101c where the TXF 101b is a transmit path filter. The receiver 104 includes a receiving unit (RX) 104a and an analog-to-digital converter (ADC) 104b. The receiving unit 104a includes an operation amplifier (OP) (not shown in the figure) and a filter circuit (not shown in the figure).
The digital signal processor 102 outputs a digital signal to the digital-to-analog converter 101a of the transmitter 101 and the digital-to-analog converter 101a converts the digital signal into an analog signal. Then, the analog signal is transmitted to a Telephone line via being processed by other circuits: the transmission filter 101b, the line driver 101c of the transmitter 101 and the transformer 103. Further the xDSL 100 receives a signal from the Telephone line via the transformer 103 and the receiving unit 104a and the analog-to-digital converter 104b of the receiver 104, and the received signal is converted into a digital signal by the analog-to-digital converter 104b and transmitted to the digital signal processor 102.
Since the Telephone line is low resistance and high load about 50˜150 ohm, the output stage (line driver 101c) of the transmitter 101 of the xDSL 100 needs large power to drive the load of the Telephone line and to maintain high linearity. In general, in order to maintain or increase linearity of the line driver 101c, more power or more area is required. However, large power consumption of the line driver 101c may not conform to an increasingly stringent power saving regulation. Therefore how to maintain the line driver 101c under acceptable performance but low power consumption becomes an important design target. Especially, since there are numerous ports in end offices, reducing power consumption is a problem which needs to be solved.